ABSTRACT
The complete gene for merozoite surface protein-1 (MSP-1) from Plasmodium berghei has been cloned and sequenced. Comparison of the P. berghei MSP-1 sequence with MSP-1 from other rodent parasites reveals five conserved domains interrupted by four variable blocks. These variable blocks exhibit no sequence homology but do have similar amino acid compositions. Primary proteolytic processing sites are located near the boundaries between the conserved domains and the variable blocks. Sequencing of the variable blocks from several P. berghei isolates shows that the predominant intra-species difference is in the number of tandem repeats. The inter- and intra-species differences suggest that the variable blocks are localized areas with relatively high levels of slipped-strand mispairing, unequal crossing-over, or other intragenic recombination activity. MSP-1 from P. berghei exhibits more repetitiveness than MSP-1 from other species suggesting that P. berghei experiences a higher intrinsic level of events producing variable numbers of tandem repeats or a lower level of events leading to the degeneration of tandem repeats.
Subject(s)
Genetic Variation , Plasmodium berghei/genetics , Protein Precursors/genetics , Protozoan Proteins/genetics , Amino Acid Sequence , Animals , Base Sequence , Cloning, Molecular , Genes, Protozoan , Merozoite Surface Protein 1 , Molecular Sequence Data , Sequence Analysis, DNA , Sequence Homology, Amino Acid , Sequence Homology, Nucleic Acid , Species SpecificitySubject(s)
Plasmodium berghei/metabolism , Protein Precursors/metabolism , Protein Processing, Post-Translational , Protozoan Proteins/metabolism , Amino Acid Sequence , Animals , Consensus Sequence , Conserved Sequence , Merozoite Surface Protein 1 , Molecular Sequence Data , Sequence Homology, Amino Acid , Species SpecificityABSTRACT
A repetitive region of Plasmodium berghei merozoite surface protein-1 (PbMSP-1) was expressed as a fusion protein with either maltose binding protein or the B subunit of heat-labile enterotoxin from Escherichia coli. Vaccination of mice with the fusion proteins indicates that this region of PbMSP-1 is antigenic as evidenced by an antibody response. The fusion proteins were also expressed in Salmonella and mice were orally immunized with the recombinant Salmonella. Some of the vaccinated mice survived a challenge with P. berghei blood-stage parasites without developing parasitemia. All control mice became patent and succumbed to the challenge infection. This partial protection was also observed with purified recombinant protein and was independent of the adjuvant used. Mice immunized with recombinant Salmonella showed either extremely low or no antibody response to PbMSP-1, suggesting that cell-mediated immunity is important for the observed protection. These studies show that it is feasible to develop a cost effective oral vaccine against the blood stage of the malarial parasite.
Subject(s)
Antigens, Protozoan/immunology , Plasmodium berghei/immunology , Protein Precursors/immunology , Protozoan Proteins/immunology , Protozoan Vaccines/immunology , Vaccines, DNA/immunology , Administration, Oral , Amino Acid Sequence , Animals , Antibodies, Protozoan/biosynthesis , Antigens, Protozoan/chemistry , Antigens, Surface/chemistry , Antigens, Surface/immunology , Conserved Sequence , Fluorescent Antibody Technique, Indirect , Immunization , Immunoblotting , Malaria/prevention & control , Merozoite Surface Protein 1 , Mice , Mice, Inbred BALB C , Molecular Sequence Data , Parasitemia/prevention & control , Precipitin Tests , Protein Precursors/chemistry , Protozoan Proteins/chemistry , Protozoan Vaccines/administration & dosage , Recombinant Fusion Proteins/chemistry , Recombinant Fusion Proteins/immunology , Repetitive Sequences, Nucleic Acid , Salmonella/genetics , Sequence Alignment , Vaccines, DNA/administration & dosageABSTRACT
Indirect fluorescent antibody (IFA) tests and enzyme-linked immunosorbent assays (ELISA) were used to measure antibodies to Plasmodium falciparum in patients with acute malaria from Bolivar State, Venezuela. Antibody titers increased significantly with repeated malarial episodes. IgG antibody responses to 4 synthetic peptides (termed C2, C3, C5, C10) derived from a 70 kDa P. falciparum (Indochina I/CDC strain) exoantigen were evaluated by a peptide-ELISA with overall positivity rates of 20%, 40%, 20% and 58%, respectively. Seropositivity to peptide C10 was consistently over 50% (range 53-75%) among patients of different ages. Overall IgM reactivity to the respective peptides was 53%, 30%, 83% and 70%. IgM reactivity was generally greater in patients with primary malarial infections. The ELISA is a useful adjunct to the IFA in measuring naturally-occurring antibodies to specific parasite proteins.
